Hello BerndG
most people just copy the whole wwwroot directory structure over to some other directory and start to modify what is there.

As you can see properties of a webpage with a right-click in a browser as well as view the source code, I don't think documentation about individual html files will help much.

Many of the html (and inc) files have documentation included ( <!-- html comment, not visible on the webpage --> ). Just have a look at them, open the files using notepad or any other editor of your preference.

If you need information about how to edit html pages, you will find excellent information here: http://www.selfhtml.org/